The physalaemin-like peptide (PSLI) extracted from the mammalian gastrintestinal tract was also found in trachea of several species by radioimmunoassay and molecular sieving chromatography. A partial purification scheme has been developed for rabbit stomach which utilizes lyophilized tissue, extraction in boiling ion formic acid, filtration or centrifugation, ethanol solbuilization and concentration, G-25 or P-4 chromatography, and LH-20 chromatography. The phase using immunoaffinity chromatography is under development. Recovery at each step varies from 70-95%, however, on reverse-phase HPLC, that value is 5-10%. Linear gradients on HPLC resolved PSLI from the amphibian peptide physalaemin which has a considerably longer retention time. Preliminary physiological experiments with HPLC-purified PSLI using the isolated guinea-pig ileum assay demonstrated a contractile response that appeared less than that of the amphibian peptide.